1. Field of the Invention
The present invention relates to a control apparatus for controlling an air conditioning unit in a motor vehicle to air-condition the passenger's compartment of a motor vehicle using internal and external power sources to achieve a comfortable riding environment in the passenger's compartment before the motor vehicle starts to run.
2. Description of the Related Art
Motor vehicles are equipped with an air conditioning unit for controlling the temperature, humidity, air flow, etc., in the passenger's compartment to keep the driver and passengers comfortable.
The air conditioning unit installed in a motor vehicle which is powered by an internal combustion engine is unable to start operating unless the engine is in operation. Therefore, if the engine is not in operation, then the driver or passengers are subject to uncomfortable conditions, e.g., an undesirable temperature or humidity, when they get into the motor vehicle. Since the start of the air conditioning unit may be delayed until the engine is readied to produce normal power or it may take a considerable period of time to be able to supply a sufficient amount of warm or cool air into the passenger's compartment, it is usually difficult to obtain a comfortable riding environment in the passenger's compartment as soon as the driver or passengers get into the motor vehicle.
To solve the above problems, it has been proposed in Japanese laid-open patent publication No. 3-42325 for a control apparatus to learn an optimum temperature and other parameters for the passenger's compartment of an automobile, and automatically start the engine of the automobile based on the learned information to adjust the temperature, humidity, etc. in the passenger's compartment.
However, because the engine is automatically started without being attended by the driver, the proposed arrangement imposes safety problems, and the fuel which is required to propel the automobile is wasted before the automobile actually starts moving.
There has been proposed an air conditioning control apparatus which employs an external power source connected to a motor vehicle to actuate an air conditioning unit before the driver gets into the motor vehicle, so that a comfortable riding environment can be attained in the passenger's compartment at a desired time when the driver gets into the motor vehicle.
The external power source is disconnected from the motor vehicle by the driver when the driver gets into the motor vehicle. However, the driver may not enter the motor vehicle immediately after the driver has disconnected the external power source from the motor vehicle. Alternatively, the external power source may be accidentally dislodged rather than being removed by the driver. At any rate, when the external power source becomes no longer available, the air conditioning unit starts being actuated by an internal power source. If the air conditioning unit is continuously actuated by the internal power source to air-condition the passenger's compartment, energy of the internal power source is unduly wasted by the air conditioning unit, possibly causing trouble when the motor vehicle actually runs.
After the driver gets into the motor vehicle, the air conditioning unit should desirably be kept in an operating condition. If the air conditioning unit were automatically turned off when a preset time has elapsed after the driver gets into the motor vehicle, the driver would have to turn on the air conditioning unit again, and would find it cumbersome to use the air conditioning control apparatus.